Thoracic
Radiographic
Anatomy
Einav Shochat MS4
Visiting Medical Student
PA and Lateral Chest Radiograph
Lobar Anatomy
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There are three lobes in the right lung and
two in the left
Lobes are divided into anatomic segments;
each is supplied by its own bronchus and
blood vessels
Lobar Anatomy:
Right upper & right middle lobes
RUL
RML
RUL
RML borders the right
atrium and much of the
dome of the diaphragm.
Indistinct borders of
these areas suggest
RML pathology.
RML
Lobar Anatomy: Right lower lobe
RLL
Consolidations of the
lower lobes are largely
behind the diaphragm
dome, hence the
diaphragm border will
still appear sharp on
the PA film.
RLL
Lobar Anatomy: Left upper lobe
LUL
LUL borders the left
atrium, left ventricle and
much of the dome of the
diaphragm. Indistinct
borders of these areas
suggest LUL pathology.
LUL
Lobar Anatomy: Left lower lobe
Most of the LLL is posterior
to the left border of the
heart and the dome of the
diaphragm. Distinct
borders of these areas with
surrounding opacity is seen
with LUL consolidations.
LLL
LLL
Can you find the source of this patient’s fever and cough?
Can you find the source of this patient’s fever and cough?
Left Lower
Lobe
pneumonia
Distinct
borders
Note the abnormal opacification of the lower vertebrae in the lateral view. Normally
there is less soft tissue around the inferior thoracic vertebrae making them appear
darker than the more superior vertebrae. See next slide for comparison.
On the right is the same radiograph from the previous slide with a normal
one for comparison.
Normally,
inferior
vertebrae
appear
darker
Note the general opacification of the lower lobe in the image on the right. Look
particularly at the vertebral bodies and posterior border of the heart.
Lobar Anatomy
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The lobes of the lungs are lined by visceral
pleura, which normally is not visualized
except along the interlobar fissures
Fissure anatomy may have many anatomic
variations and may not be complete
On the right there are two fissures, the oblique (major)
fissure and the horizontal (minor) fissure. The left lung
contains an oblique fissure only.
minor
minor
It is uncommon to see distinct fissures. If opacified
there may be thickening of or fluid between the pleura.
This patient has
congestive heart failure
and subsequent
subpleural thickening.
Can you identify the
oblique fissures?
It is uncommon to see distinct fissures. If opacified
there may be thickening of or fluid between the pleura.
This patient has
congestive heart failure
and subsequent
subpleural thickening.
Can you identify the
oblique fissures?
Here there is fluid trapped between the pleura within
the fissures.
Occasionally accessory fissures can be found. For example,
the azygos fissure, a normal variant, can form during the
embryonic migration of the azygos vein through the apical
pleura.
Knowing the normal position of the interlobar fissures helps us
diagnose pulmonary volume changes. For example when a lobe
collapses the fissure is displaced and seen as a sharp interface
between opacified (collapsed) and aerated lung.
Can you identify the pleural lining of the collapse lung?
Knowing the normal position of the interlobar fissures helps us
diagnose pulmonary volume changes. For example when a lobe
collapses the fissure is displaced and seen as an interface
between two densities (e.g., opacified/collapsed and aerated lung)
Can you identify the pleural lining of the collapse lung?
scapulae
Left pulmonary
artery:
vasculature are
pulled inferiorly by
the collapsed LLL
Major fissure not
normally seen on the PA
film because it runs parallel
to the radiation beams
Inferior
vertebrae
opacified by
LLL atelectasis
Left hemidiaphragm
becomes indistinct
when adjacent to
collapsed LLL
What’s happened here?
What’s happened here?
Right upper
lobe collapse
We can use the pleura to identify whether a mass is within
the lung parenchyma or in the extrapleural space.
Is this mass intrapleural or extrapleural? How can you tell?
We can use the pleura to identify whether a mass is within
the lung parenchyma or in the extrapleural space.
Is this mass intrapleural or extrapleural? How can you tell?
Extrapleural
The medial border of the mass is draped by pleura and is distinct where it is adjacent to
aerated lung. The lateral border is next to bone and soft tissue of more similar density.
The pleura is often involved in inflammatory and traumatic
insults to the chest. These may result in areas of thickening or
distortion of the pleural lining, which may be appreciated in
the normally sharp costophrenic & cardiophrenic angles/sulci.
Lateral
costophrenic
angle
Cardiophrenic
angle
Lateral
costophrenic
angle
Posterior
costophrenic
angle
Pleural effusions can be identified by: blunting of the lateral and
posterior costophrenic sulci, a meniscus sign, opacification of a
hemithorax, and/or fluid in the fissures.
Small free-flowing pleural effusions are best identified on the lateral radiograph
as this view captures the most dependent region of the thoracic cavity, the
posterior costophrenic angles.
Mediastinum
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Many structures can be identified within
the mediastium; we will start with the
heart and blood vessels…
How many structures can you identify?
Vascular
pedicle
SVC
Aortic pulmonary
recess
Aortic
arch
Right
pulmonary
artery
Left
LA
Right
pulmonary
artery
(lower lobe)
RA
LV
RV
How many structures
can you identify?
Brachiocephalic
vessels
Trachea
Aorta
LPA
RPA
Left upper
lobe
bronchus
Pulmonary
outflow
tract
LA
RV
IVC
Right upper
lobe bronchus
Confluence
of pulmonary
veins
LV
Right
hemidiaphragm
Gastric air
bubble
Left
hemidiaphragm
Which valve has been replaced?
Which valve has been replaced?
Aortic valve
Note the orientation of the
valve perpendicular to the
plane of the PA film.
Which valve has been replaced?
Which valve has been replaced?
Pulmonic
The pulmonary outflow
tract is more superior
and lateral than many
people think.
Last one, name the valves…
Last one, name the valves…
Aortic
Aortic
Tricuspid
Tricuspid
Mitral
Mitral
The Vascular Pedicle
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Found in the superior mediastinum.
Right and left margins are normally formed by the
superior vena cava and the descending portion of
the aortic arch, respectively.
A widened vascular pedicle can have several
etiologies including elevated intravascular volume,
aortic trauma, or pericardial effusion.
Aortic
arch
Vascular
pedicle
Superior
vena
cava
Intravascular volume
depletion
vs.
Intravascular volume
elevation
Intravascular volume
depletion
Intravascular volume
elevation
Vascular
pedicle
Vascular
pedicle
Superior
vena cava
vs.
Aorta
Superior
vena cava
Aorta
Intravascular volume elevation resulting in an expanded SVC should not be
mistaken for hematoma, which would have a less distinct border and more
opacified appearance.
Trauma patient with an aortic transection
Note the vascular pedicle’s “fuzzy”, opacified right border.
What is happening here?
What is happening here?
Looks pretty
wide eh?
Can you follow the heart borders?
What is happening here?
The wide vascular
pedicle here
results from a
pericardial
effusion
If you look closely you can
make out the superior
pericardial border
The pacemaker
wires roughly
outline the right
atrium border
effusion
The left heart border
can be seen within
the effusion
effusion
Comparing this with older films can also help make the diagnosis.
Pulmonary Airways & Vasculature
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The lungs on the normal chest radiograph
are made by pulmonary vessels, the
bronchi are normally not seen.
This is because:


Pulmonary vessels are blood-filled with density
similar to water.
Bronchi are filled with air and normally have thin
walls that do not provide contrast to aerated
lungs.
Pulmonary Airways & Vasculature
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When lung parenchyma fill with water or
inflammatory material:


Water-density vessels become less distinct.
Air-filled bronchi can be seen as “air
bronchograms”.

If airways are obstructed (e.g., tumor) they may fill
with fluid and no “air bronchograms” will be
appreciated.
How do these two radiographs differ?
How do these two radiographs differ?
Normal
well-defined
vessels
Abnormal
indistinct
vasculature
In the normal chest radiograph only airways
within the mediastinum are apparent.
Trachea
Right
mainstem
bronchus
Left
mainstem
bronchus
Trachea
Left
mainstem
bronchus
What is the source of this man’s chronic cough?
What is the source of this man’s chronic cough?
Obstruction
Horizontal
fissure
Unilateral lung
opacification
with ipsilateral
tracheal shift
from the
pressure
differential
helps identify
RUL collapse
RUL
Tented right
hemidiaphragm
Inferior pulmonary
ligament tethering the
lobe and tenting the
diaphragm
Right upper lobe collapse secondary to obstruction of
the bronchus by squamous cell carcinoma.
What is the source of this patient’s dyspnea?
What is the source of this patient’s dyspnea?
Atelectasis
Seen commonly as crowded
parallel air-bronchograms
(if airways are not obstructed)
What is abnormal here?
What is abnormal here? The patient has Sarcoidosis.
Lateral border of
the SVC is
obscured by
lymphadenopathy
Bronchus
lumen is
obscured
Think about lymphadenopathy when opacities obscure the aortic
pulmonary recess (PA) or surrounding the left distal main
bronchus (on the lateral)
Other Mediastinal Structures
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Esophagus
Thyroid
Thymus
Lymph nodes
These are generally not seen unless there
is pathology
What could be the source of this anterior mediastinal mass?
What could be the source of this anterior mediastinal mass?
Ddx: Lymphoma/leukemia, germ cell tumors (e.g., teratoma),
thymic mass (e.g., thymoma, cyst), enlarged thyroid, vascular
(e.g., hematoma, aortic aneurysm).
This patient has a thymoma.
How about this one?
How about this one?
This patient has a an enlarged thyroid gland.
Extrapulmonary Structures
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Diaphragm
Stomach/gastric bubble
Liver, spleen
Bones: clavicles, ribs, scapulae, spine
Other soft tissues
In the normal radiograph, the diaphragm is domed with the right
side higher than the left (i.e., the heart lying on the left side of
the diaphragm may contribute to the lower level).
Left
diaphragm
Right
diaphragm
Elevated intrathoracic pressures (e.g., hyperinflation
from obstructive lung disease, tension pneumothorax)
will flatten the diaphragm.
Flat
Flattened
Not many structures left, so let’s just quiz…
What’s abnormal in these films?
What’s abnormal in these films?
Notice the air
around the left and
right pulmonary
arteries.
LLL
atelectasis
The lucent stripe along the inferior heart border, crossing midline is called
a “continuous diaphragm” sign and is indicative of pneumomediastinum.
What’s abnormal in
this film?
What’s abnormal in
this film?
Free air
Normally the only air
we see under the
diaphragm is in the
gastric bubble and
bowels.
Subdiaphragmatic
free air is indicative of
perforated viscus.
What’s abnormal in this film?
What’s abnormal in this film?
Hiatal
hernia
This hiatal hernia is easier to see with the gastric
air bubble behind the heart.
What’s abnormal in this film?
What’s abnormal in this film?
Tracheal deviation
Gastric
bubble,
bad sign
Ruptured
diaphragm
What’s abnormal in this film?
What’s abnormal in this film?
Splenomegaly
Gastric air bubble
What’s abnormal in this film?
Gastric air bubble
What’s abnormal in this film?
Ouch
Gastric air bubble
Which patient needs a chest tube?
Gastric air bubble
Which patient needs a chest tube?
Pneumothorax
Scapula
medial
border
Skin fold
lateral border
To decide whether a line in the lung
represents the scapula, a skin fold
or a pneumothorax consider the
density difference between the two
sides of the line. A pneumothorax
will have a sharp line with air density
(equal density) on both sides. Skin
or scapula will have a line with air
on one side and more opaque tissue
Gastric air bubble
on the other.
What’s abnormal in this film?
What’s abnormal in this film?
Nothing
The left lung
appears more
opacified but it
is the result of
uneven
radiation.
The patient is rotated slightly causing the “heel effect”, the relative over exposure of
one hemithorax compared to the other caused by uneven radiation. Looking at the
relative exposure of the extrathoracic soft tissues can help identify the “heel effect”.
References:
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Collins J, Stern EJ. Chest Radiology, the
Essentials. Lippincott, Williams & Wilkins. 1999.
Dafner RH. Clinical Radiology, the Essentials. 2nd
Ed. Lippincott, Williams & Wilkins. 1999.
Freindlich IM, Bragg DG. A Radiologic Approach
to Diseases of the Chest. 2nd Ed. Williams &
Wilkins. 1997.